The present invention relates to a fluorescent lamp and a method for manufacturing it.
Conventional fluorescent lamps have amalgam in an arc tube for controlling mercury vapor pressure during its operating. In order to obtain an optimal mercury vapor pressure, this amalgam needed to be placed in an atmosphere with an appropriate temperature.
Therefore, according to a conventional amalgam type fluorescent lamp shown, for example, in JP62(1987)-43452U, an exhaust pipe 22, which extends from an end portion of a bulb 17 and is cut and sealed at its point, contains amalgam 25 and also a glass rod 24 for supporting this amalgam 25 so that the amalgam 25 does not enter a discharge space and for controlling the position of this amalgam 25. This amalgam 25 is located between the glass rod 24 and the point of the exhaust pipe 22.
In manufacturing such a conventional amalgam type fluorescent lamp, if the two elements, i.e. the glass rod 24 and the amalgam 25, are to be contained in an appropriate portion of the exhaust pipe during or after an exhaust process, the exhaust equipment becomes complicated. Furthermore, such the equipment tends to cause unevenness of quality. In order to avoid these problems, a method applied hereto includes the process of positioning the glass rod 24 and the amalgam 25 in the appropriate portion of the exhaust pipe immediately before the exhausting process. In this process, air contained in the bulb is exhausted through the exhaust pipe, then, the lamp is introduced a filler gas, and cut and sealed the appropriate portion of the exhaust pipe. Moreover, in this exhaust process, the bulb is heated in order to exhaust the impure gas efficiently.
However, such a conventional amalgam type fluorescent lamp has the following problems. The amalgam sometimes melts due to the heat applied during the exhaust process or during its operating, and this molten amalgam flows into the space between the exhaust pipe and the glass rod. As a result, the position of the amalgam is shifted from the appropriate location inside the exhaust pipe, thus the lamp loses the luminous efficiency.
Furthermore, another problem is that, in the exhaust process, solid amalgam tends to be drawn into the exhausting equipment. There is also another problem that, when the amalgam melts, a part of mercury contained in the amalgam evaporates, which then is exhausted together with the residual air. As a result, the amount of mercury sealed inside the lamp is reduced to insufficient level.
Moreover, the glass rod placed in the exhaust pipe slows down vacuum pumping speed in the exhaust process because the glass rod also acts as an obstacle. Thus, deterioration of exhaust efficiency becomes remarkable and longer duration of exhaust time is needed.
It is an object of this invention to avoid the previous problems described above by preventing amalgam outflow into the exhausting equipment in the exhaust process and obtaining high luminous efficiency by maintaining optimal mercury vapor pressure.
Furthermore, it is another object of this invention to provide a method of manufacturing a fluorescent lamp having better working efficiency and exhaust efficiency suppressing the excess reduction of the total mercury amount filled inside a bulb.
The fluorescent lamp of this invention has an amalgam container, which is arranged inside an exhaust pipe extending from an end portion of a bulb to which electrodes are attached at both end portions. The amalgam container contains amalgam inside and has an opening portion through which the contained amalgam cannot go out and stays the amalgam in the proper position. The opening portion of the container is located on the side where the exhaust pipe is cut and sealed.
According to this configuration, in the exhaust process of manufacturing, the amalgam placed inside the bulb cannot flow into an exhaust equipment. In addition, even if the amalgam melts during the exhaust process or during lamp operating, it stays in an appropriate position. As a result, the mercury vapor pressure inside the bulb is maintained optimally during lamp operating.
In the fluorescent lamp of the above configuration, it is better that a maximum distance between the amalgam container and the inside of the exhaust pipe is in the range between 0.1 mm and 2.0 mm. Because, at the start of operation, the mercury vapor should be released smoothly from the amalgam container into a discharge space. At the same time, breakage of the exhaust pipe is prevented because the amalgam container does not bump into the exhaust pipe during the transportation of the lamps and so forth.
Furthermore, in the fluorescent lamp of the above configuration, it is better that a distance between the amalgam and the electrode is in the range between 20 mm and 50 mm. Thereby, during lamp operating, the mercury vapor is supplied appropriately by the amalgam, so that the mercury vapor pressure inside the bulb is controlled optimally.
Moreover, in the fluorescent lamp of the above configuration, it is more better that the amalgam container has a through hole for connecting a space where the amalgam is contained and a discharge space. Thereby, at the start of operation, the mercury vapor is released more smoothly from the amalgam container into the discharge space.
The method for manufacturing the fluorescent lamp of this invention is for any one of the fluorescent lamps mentioned above, including (a) exhausting air inside the bulb and (b) cutting and sealing an appropriate portion of the exhaust pipe after the step (a), wherein the amalgam container containing the amalgam is settled in the appropriate portion of the exhaust pipe at a point of change from the step (a) to the step (b).
Due to this configuration, it is no longer necessary to settle a glass rod and an amalgam separately in the appropriate portion of the exhaust pipe as before. Therefore, working efficiency is improved without making the exhaust equipment complicated. Furthermore, in the exhausting step (a), there is nothing inside the exhaust pipe, therefore, the exhaust efficiency is improved. Moreover, the amalgam is not affected by heat during the exhausting step (a). In other words, the mercury does not evaporate from the amalgam during the exhausting step (a), and the mercury vapor is not exhausted together with the residual gas. As a result, the excess reduction of the total mercury amount filled inside the bulb is suppressed.
In the method mentioned above, it is more better that, after the amalgam container is settled in the exhaust pipe, the exhaust pipe should be cut and sealed within 30 seconds. By this, the thermal effect on the amalgam is reduced, and the excess reduction of the total mercury amount filled inside the bulb is suppressed even more.